1. Field of the Invention
The present invention relates to a heat-assisted magnetic recording head for use in heat-assisted magnetic recording where a recording medium is irradiated with near-field light to lower the coercivity of the recording medium for data recording.
2. Description of the Related Art
Recently, magnetic recording devices such as a magnetic disk drive have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a reproducing head including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a recording head including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider which flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data recording with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technique so-called heat-assisted magnetic recording. This technique uses a recording medium having high coercivity. When recording data, a magnetic field and heat are simultaneously applied to the area of the recording medium where to record data, so that the area rises in temperature and drops in coercivity for data recording. The area where data is recorded subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization.
In heat-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to irradiate a plasmon antenna, which is a small piece of metal, with laser light. The plasmon antenna has a near-field light generating part which is a sharp-pointed part for generating near-field light. The laser light applied to the plasmon antenna excites surface plasmons on the plasmon antenna. The surface plasmons propagate to the near-field light generating part of the plasmon antenna, and the near-field light generating part generates near-field light based on the surface plasmons. The near-field light generated by the plasmon antenna exists only within an area smaller than the diffraction limit of light. Irradiating the recording medium with the near-field light makes it possible to heat only a small area of the recording medium.
In general, the laser light to be used for generating the near-field light is guided through a waveguide that is provided in the slider to the plasmon antenna that is located near the medium facing surface of the slider. Possible techniques of placement of a light source that emits the laser light are broadly classified into the following two. A first technique is to place the light source away from the slider. A second technique is to fix the light source to the slider.
The first technique is described in U.S. Patent Application Publication No. 2006/0233062 A1, for example. The second technique is described in U.S. Patent Application Publication No. 2008/0055762 A1, U.S. Patent Application Publication No. 2008/0002298 A1, and JP 2008-16096 A, for example.
The first technique requires an optical path of extended length including such optical elements as a mirror, lens, and optical fiber in order to guide the light from the light source to the waveguide. This causes the problem of increasing energy loss of the light in the path. The second technique is free from the foregoing problem since the optical path for guiding the light from the light source to the waveguide is short.
The second technique, however, has the following problem. Hereinafter, the problem that can occur with the second technique will be described in detail. The second technique typically uses a laser diode as the light source. The laser diodes available include edge-emitting laser diodes and surface-emitting laser diodes. In an edge-emitting laser diode, the emission part for emitting the laser light is located in an end face that lies at an end of the laser diode in a direction parallel to the plane of an active layer. The emission part emits the laser light in the direction parallel to the plane of the active layer. In a surface-emitting laser diode, the emission part for emitting the laser light is located in a surface that lies at an end of the laser diode in a direction perpendicular to the plane of the active layer. The emission part emits the laser light in the direction perpendicular to the plane of the active layer.
The laser light emitted from a laser diode can be made incident on the waveguide by a technique described in U.S. Patent Application Publication No. 2008/0055762 A1, for example. This publication describes arranging an edge-emitting laser diode with its emission part opposed to the incident end of the waveguide so that the laser light emitted from the emission part is incident on the incident end of the waveguide without the intervention of any optical element. According to this technique, the laser diode is arranged so that the longitudinal direction of the laser diode, i.e., the direction of the optical axis of the laser light to be emitted from the emission part, is perpendicular to the end face of the slider where the incident end of the waveguide is located. In such a case, the laser diode needs to be positioned with high precision so that the optical axis of the laser light emitted from the emission part will not tilt with respect to the optical axis of the waveguide. If the optical axis of the laser light emitted from the emission part tilts with respect to the optical axis of the waveguide, the laser light may fail to be delivered to the plasmon antenna with sufficient intensity. When the laser diode is to be arranged so that the longitudinal direction of the laser diode is perpendicular to the end face of the slider where the incident end of the waveguide is located, however, there is a problem that the longitudinal direction of the laser diode can easily tilt with respect to the direction perpendicular to the end face of the slider where the incident end of the waveguide is located, and it is thus difficult to align the laser light with the waveguide.
JP 2008-16096 A describes a head that has a unit substrate with an edge-emitting laser diode attached thereto and a propagation layer for guiding laser light emitted from the laser diode to the incident end of the waveguide, the unit substrate and the propagation layer being arranged on a rear surface of the slider opposite to the medium facing surface. In this head, the laser diode emits laser light in a direction parallel to the rear surface. The propagation layer has a total reflection surface for changing the direction of travel of the laser light emitted from the laser diode. In the head, the distance from the laser-light emission part of the laser diode to the total reflection surface and the distance from the total reflection surface to the incident end of the waveguide are both relatively long. In consequence, the laser light can be too large in diameter at the position of the incident end of the waveguide, so that part of the laser light may fail to enter the waveguide and the amount of the laser light to propagate through the waveguide may thus decrease.
The laser light emitted from a laser diode may be made incident on the waveguide by other techniques. For example, U.S. Patent Application Publication No. 2008/0002298 A1 describes a technique in which a surface-emitting laser diode is arranged with its emission part opposed to the surface of the slider on the trailing side so that the laser light emitted from the emission part is incident on the waveguide from above. This technique facilitates aligning the laser light with the waveguide. Surface-emitting laser diodes, however, typically have a lower optical output as compared with edge-emitting laser diodes. The technique therefore has the problem that it is difficult to provide laser light of sufficiently high intensity for use in generating the near-field light.